This competitive revision R03 application is in response to Notice Number (NOT-OD-10-032) and Notice Title: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications (R01, R03, R15, R21, R21/R33, and R37) through the NIH Basic Behavioral and Social Science Opportunity Network (OppNet). The neurotransmitter dopamine plays an important role in the brain reward process. Dysfunction of the dopaminergic system is implicated in addictive behaviors. The relationship between dopaminergic system and cocaine addiction has been well characterized. Numerous studies have shown that the D1 dopamine receptor subtype is involved in mediating the effects of cocaine. Acute and chronic administration of cocaine alters the expression levels of D1 receptors in the mesocorticolimbic pathway. The molecular mechanisms and extracellular factors that mediate the changes in D1 receptor expression in cocaine-treated animals are largely unknown;however some reports have indicated that changes occur at the post-transcriptional level. In the parent R03 project, we are testing a novel hypothesis that posttranscriptional modulation of D1 dopamine receptor expression is mediated by microRNAs that bind cis- acting elements in the 3'untranslated region (3'UTR) of the D1 receptor mRNA. The goal of the parent R03 project is to determine if cocaine-induced changes in D1 receptor expression can be related to changes in expression of a specific microRNA, and to demonstrate, using primary cultures of D1 receptor-expressing neurons, that altering the expression of this microRNA will also alter the expression of D1 receptor protein. One year into the project, we have determined that D1 receptor exhibits post transcriptional regulation in a brain region-specific manner in juvenile mice. Quantitative microRNA profiling in the caudate has identified 139 microRNAs that show a greater than 3-fold change in expression following 7 days of cocaine treatment. A subset of these microRNAs (10) show increased expression AND have putative binding sites in the D1 3'UTR, implicating them in D1 receptor posttranscriptional regulation. In this revision application, we test a new hypothesis that in mice that exhibit cocaine-induced behavior sensitization, a cocaine challenge will elicit a rapid alteration in microRNA-mediated posttranscriptional regulation of D1 receptors, increasing D1 protein expression and contributing to the increased locomotor activity. The goal of the proposed experiments is to temporally relate potential rapid changes in microRNA-mediated posttranscriptional regulation to changes in cocaine-induced locomotor behavior. The revision application meets the goals of OppNet and the Recovery Act, as it incorporates behavioral paradigms into the parent R03 project, requests funds for behavioral testing equipment and adds new personnel to assist with the behavioral experiments. The results from this project will improve our understanding of molecular mechanisms that regulate changes in dopamine receptor expression in cocaine addiction in particular, and addictive processes in general. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to determine the role of microRNAs in mediating regulation of D1 dopamine receptor expression in cocaine-induced behavior sensitization. The project will identify microRNAs that are involved in the sensitization process and determine if the levels of these microRNAs control the post- transcriptional regulation of D1 receptor expression following cocaine challenge. The results of this proposal will open a new area of research in dopamine receptor biology and lead to the development of potentially novel therapeutic methods for treating cocaine addiction.